Hi Bob,
The key here is "(assuming the plunger was clean, true, no nicks, burrs,
etc.)?" It appears that in reality, many valves are not fully seated.
Maybe due to non concentric wear of the seat, hydraulic erosion,
contamination, or what ever, even small leaks will greatly reduce idle
pressure. Correcting the seating & or increasing spring pressure can
make a big difference in seating & on idle pressure. At higher pump
speeds/outputs, the small seating leaks will have proportionately less
effect. Oil flow requirements do not increase nearly as much with rpm
increase as does pump output.
The seating "could be" improved by lapping the two mating parts, but I
wouldn't suggest it unless it is complete rebuild where the lapping
compound could be completely removed. This is something that I always check.
In the case under discussion, the spring apparently is noticeably
shorter & probably less tension than the original. As stated, shimming
is likely to be as good or better fix than just replacing the spring
with an unknown one.
Dave Russell
Bob Spidell wrote:
> OK, I'm cornfused. The pressure relief valve is meant to limit
> maximum oil pressure, why would it raise idle pressure (assuming the
> plunger was clean, true, no nicks, burrs, etc.)? That is, the relief
> valve should be closed withing a few psi of the max. allowed pressure
> (granting a few psi "wiggle room"). It should be fully closed and
> seated well above the pressure put out by the pump at idle, so
> pressure at idle will be determined by pump, bearings, bushings, etc.
> Or am I missing something?
>
>
> bs ***************************************************************
> Bob Spidell San Jose, CA bspidell@comcast.net '67
> Austin-Healey 3000 '56 Austin-Healey 100M
> ***************************************************************
>
> Subject: Re: Oil Pressure Relief Valve Spring (One More Time!)
>
>
>> Hi Russ,
>>
>> All springs tend to fatigue a bit over time. It would certainly do
>> no harm to replace the spring. The only unknown, is the tension &
>> quality of the replacement spring. A simple experiment would be to
>> place a spacer under the existing spring. I believe there is room
>> for up to an additional .250" long spacer between the spring & it's
>> cap. (Too long A spacer will cause spring coil bind & prevent the
>> relief port from uncovering to control the pressure.)
>>
>> Also try to make sure that the plunger & it's seat are clean, free
>> of burrs, & actually fully seating. Tapping the plunger into it's
>> seat with a wood dowel often helps. More spring pressure can
>> actually improve a leaking valve seat & boost idle pressure as well
>> as running pressure.
>>
>> On my BN2, a .160" spacer gave 25-45psi hot idle - run. A .360
>> spacer gave 40-60 psi hot idle - run. The max cold run pressure
>> does not exceed 60. I'm not sure if the .360" spacer would allow
>> full relief valve travel on your specific engine, thus the
>> previously mentioned .250" spacer limitation. It would be easy to
>> determine if the spacer was too long. The cold max pressure would
>> be too high.
>>
>> Dave Russell
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